Metal composite

ABSTRACT

A metal composite of a major constituent metal such as titanium, columbium, zirconium, hafnium, tantalum which has dispersed in it a minor constituent of thorium oxide particles is disclosed, along with the process for manufacturing the metal composite. The particles are formed in situ by the reaction of thorium and oxygen. The oxygen is usually added as an oxide of the major constituent metal but may be introduced in other ways. Thorium oxide particles usually comprise from a fractional mole percentage to more than 4 mole percent of the metal composite.

United States Patent [191 Dohogne METAL COMPOSITE Charles Leroy Dohogne, 29615 Enrose Ave., San Pedro, Calif. 90732 221 Filed: Sept. 7, 1971 21 Appl. No.: 178,378

[76] Inventor:

[52] US. Cl 75/175.5, 75/135, 75/174, 75/177 [51] Int. Cl. C22c 15/00, C220 27/00 [58] Field of Search 75/O.5 BB, 0.5 BA, 0.5 BC, 75/134, 135, 174, 175.5, 177; 148/32 [451 Apr. 30, 1974 Primary ExaminerCharles N. Lovell Attorney, Agent, or FirmFowler, Knobbe & Martens ABSTRACT A metal composite of a major constituent metal such as titanium, columbium, zirconium, hafnium, tantalum which has dispersed in it a minor constituent of thorium oxide particles is disclosed, along with the process for manufacturing the metal composite. The particles are formed in situ by the reaction of thorium and oxygen. The oxygen is usually added as an oxide of the major constituent metal but may be introduced in other ways. Thorium oxide particles usually comprise from a fractional mole percentage to more than 4 mole percent of the metal composite.

3 Claims, N0 Drawings METAL COMPOSITE This invention relates to metallurgical compositions and processes. More specifically, this invention relates to composites of certain metals, titanium in particular, and metallurgically similar metals such as columbium, zirconium, hafnium, and tantalum, which are hardened and made more resistant to loss of stability at high temperatures, without loss of malleability, by the in situ formation of thorium oxide in these metals.

Improved physicalproperties have been shown in certain metal systems by the fine dispersion of hard, nonreactive, nonmetallic second phases. This is notably true in the T. D. Nickel, S. A. P. Aluminum and thorium dispersed lead alloys. Several advantages may flow from this approach. Among these advantages are reduced grain size, increased yield strength, improved creep and fatigue resistance, and more favorable high temperature properties.

British and, more recently, American alloys are available based upon the titanium-silicon system. These alloys, however, have not achieved notable success beity. These alloys are perhaps most accurately referred to as precipitation hardened alloys.

In general, efforts to provide high temperature stability have resulted in loss of hardness, strength, or malleability. The disadvantages of previous metallurgical systems are overcome by the present invention which provides a moderate hardening effect and significantly improved high temperature resistance without loss of malleability necessary for forming operations.

I have now discovered that thorium oxide formed in situ as a minor constituent of a titanium metal system provides significantly increased high temperatureresistance and hardness without loss of desired formability and malleability.

According to the principle feature of this invention, then, a titanium, or a similar metallurgical system, is modified by the in situ reaction of a minor proportion of the thorium with oxygen to form thorium oxide which is substantially uniformly dispersed throughout the major metal constituent, titanium for example. The process and the resulting product are important features of this invention.

In general, the processis carried out in a major constituent metal selected from the group which consists of titanium and metals having similar metallurgical properties; columbium, zirconium, hafnium and tantalum. Hereinafter, the titanium is given as exemplary of the reaction and major constituent metals involved. The major constituent metal may include up to 10 percent or l2 percent, by weight, of an alloying metal.

Sufficient thorium is added to the major constituent metal along with an oxygen donor in sufficient quantities to provide a minorconstituent of thorium oxide. Thorium acts in situ with the oxygen to form thorium oxide particles which have been found to be substantially uniformly dispersed throughout the major constit-' uent metal system.

The resulting product has increased hardness, substantially improved heat stability and yet retains sufficient malleability for easy machining and working.

In carrying out the process, in the exemplary embodiments described herein, thorium is reacted with oxygen in a system in which titanium is the major constituent. By the term major constituent, I mean a system in which titanium, or the similar metals previously named,

and alloying metals constitute percent or more, by weight, and preferably 94 percent or more, of the system. The major constituent may include up to lO-l2 percent alloying metals.

The oxygen is supplied to the system, normally, as titanium oxide, or as the oxide of an alloying metal or another metal which can be present in the system in small quantities without significantly disturbing the metallurgical properties of the major constituent metal and the ultimate system. Thus, the composition consists essen tially of the major constituent metal (including alloying metals) and thorium oxide with a slight excess of oxygen or thorium depending upon which of these minor constituents limits the amount of thorium oxide formed.

The oxygen can, however, be added directly during the melting process, if desired; however, this procedure is inconvenient and provides no known advantage over adding oxygen by way of an oxygen donor such as the oxide of a major constituent metal.

In the preferred embodiment of the process as presently developed, a mixture of titanium, titanium containing oxygen, and thorium are melted in a vacuum fumace, typically the consumable arc type of furnace conventionally used in ,reactive metal working. The thorium reacts with the oxygen in the titanium oxide to produce a more stable oxide compound, thorium oxide, ThO The thorium oxide thus formed in situ is substantially uniformly dispersed as a second phase. To date, no excessive segregationin grain boundaries has been observed and no significant variation from uniform dispersion has been noted. Thorium oxide particles are generally in the size range of about 0.05 to 0.1 micron. Whether all processes result in this particle size of thorium oxide has not been determined and, likewise, the effect of particle size of the minor constituent, thorium oxide, has not been studied but it has been established that where the in situ formed thorium oxide has a particle size in the general range of about 0.050.l micron, average, the desired characteristics of the composition result.

The desired characteristics of the composition result with thorium oxide present as a dispersed particulate minor constituent in the range of about 0.0 l 5 mole percent to more than 4 mole percent thorium oxide. The preferred and presently believed to be the most efficacious range thorium oxide concentration is from about 1 mole percent to about 3 or 4 mole percent.

The following examples will serve to illustrate the preferred embodiment of the invention but are given not as limitative of the invention but as illustrative of the method and composition of the invention.

EXAMPLE I Control Commercially available high purity titanium sponge was melted, cooled, cut and metallurgically polished. Examination by scanning electron microscope revealed no second phase. Titanium-Thorium Oxide System A mixture consisting of 93.23 percent of the commercial titanium sponge used in the control, 5.85 weight percent thorium and 0.92 weight percent oxygen was melted, cooled, cut and metallurgically polished. Examination by scanning electron microscope shows the existence of a finely divided, uniformly dispersed second phase.

Melting in both instances was by the consumable arc method in vacuum.

EXAMPLE [1 Control A A 60 gram specimen of commercial high purity titanium sponge was melted in the furnace, using the conventional technique. The resultant button showed the typical large columnar grain structure. Hardness was below the Rockwell C scale measurement range, but the indentation showed no cracking under 600)( microscopic examination. Control B A 60 gram specimen of the same commercially pure titanium sponge is melted with titanium oxide in an amount equivalent to a 3 mole percent TiO The resultant button showed excessively large columnar grain structure. Hardness was measured at 22 on the Rockwell C scale with cracking around the indentations, showing very low ductility. Titanium-Thorium Oxide Composition Another 60 gram specimen of the same commercial titanium sponge was melted with titanium oxide and thorium metal sufficient to produce 3 mole percent ThO using the conventional equipment and technique. The resultant button showed a fine equiaxial grain structure. Hardness was measured at 26 on the Rockwell C scale with no cracking visible at 600K magnification. A scanning electron microscopic study was made at 2,000X, 5,000X and 10,000X. This study showed a dispersion of particles equally dispersed in the grains and grain boundaries. The particle size was about 0.1 micron average diameter.

The titanium-thorium oxide composition was found to have unexpectedly high stability at high temperatures and, as the foregoing microscopic examination demonstrated, to retain the ductility necessary for easy handling and fabrication.

As the foregoing specification including examples demonstrates, a new process and composition consisting essentially of a major constituent of titanium or similar metals such as columbium, zirconium, hafnium and tantalum, and a minor constituent of uniformly dispersed thorium oxide possesses useful and unique properties. It will be understood in regard to the specific embodiment described, and in particular with respect to the examples, that this disclosure is illustrative of the invention and does not limit the invention to the specific examples disclosed. The scope of the invention, therefore, is limited only by the following claims.

What is claimed is:

1. A process for forming malleable, hardened temperature stable metal composite consisting essentially of mixing a major constituent metal selected from the group consisting of titanium, columbium, zirconium, hafnium and tantalum, an oxide of the major constituent metal, and thorium, and melting said mixture under inert conditions to cause the oxide to react in situ with the thorium to form from about 0.015 to about 4 mole percent thorium oxide particles dispersed in said major constituent metal.

2. The process defined in claim 1 wherein the major constituent is titanium.

3. The process defined in claim 2 wherein the major constituent contains from about 1 mole percent to about 3 mole percent dispersed thorium oxide, and the thorium oxide particles have an average size of about 0.1micron. 

2. The process defined in claim 1 wherein the major constituent is titanium.
 3. The process defined in claim 2 wherein the major constituent contains from about 1 mole percent to about 3 mole percent dispersed thorium oxide, and the thorium oxide particles have an average size of about 0.1 micron. 